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How to Adjust Generator Voltage by AVR

Aug. 18, 2020

AVR (Automatic voltage regulator) is an instrument that adjusts voltage by means of automatic control device.

Voltage regulator (referred to as AVR) is designed for AC brushless generators with fundamental wave, harmonic compound excitation or permanent magnet generator excitation (PMG system).

Voltage regulator realizes the automatic regulation of generator output voltage by controlling the excitation current of generator AC exciter. Generator voltage regulator can be used for ordinary 60/50Hz as well as medium frequency 400Hz single or parallel generators.

An AVR is at the heart of devices often called power conditioners or power stabilizers. The typical power conditioner is an automatic voltage regulator combined with one or more other power-quality capabilities, such as:

1) Surge suppression

2) Short circuit protection (circuit breaker)

3) Line noise reduction

4) Phase-to-phase voltage balancing

5) Harmonic filtering, etc.

Power conditioners are typically used in low voltage (<600V) applications and sizes below 2,000KVA.

In general, the AC automatic voltage regulator (AVR) is a device designed to regulate voltage automatically – that is, to take a fluctuating voltage level and turn it into a constant voltage level.


Working principle of AVR

The voltage regulator is an adjustment device that controls the generator output voltage within a specified range. Its function is to automatically control the generator voltage and keep it constant when the rotating speed of the generator changes, so as to prevent the generator voltage from being too high to burn out the electrical equipment and cause the battery to overcharge. At the same time, it also prevents the generator voltage from being too low, resulting in malfunctioning of electrical equipment and insufficient battery charge.

Since the transmission ratio of generator to engine is fixed, the speed of generator will change with the change of engine speed. The power supply of generator to electric equipment and charging to battery both require its voltage to be stable, so it is necessary to adjust the output voltage of generator if the voltage is kept at a certain value basically.

A synchronous generator regulator that maintains the synchronous generator voltage at a predetermined value or changes the terminal voltage as planned.

When the terminal voltage and reactive power of the synchronous motor change, the output current of the exciter is automatically controlled according to the corresponding feedback signal to achieve the purpose of automatically regulating the terminal voltage or reactive power of the synchronous motor.

According to the working principle, the voltage regulator of alternator is divided  into:

1. Contact type voltage regulator

Contact type voltage regulator was applied earlier, the regulator contact vibration frequency is slow, there is mechanical inertia and electromagnetic inertia, voltage regulation accuracy is low, contact is easy to generate sparks, large radio interference, poor reliability, short life, now has been eliminated.

2. Transistor regulator

With the development of semiconductor technology, transistor regulator is adopted. The advantages is high switching frequency of triode, no sparks, high adjusting precision, light weight, small volume, long life, high reliability, small radio interference and so on. Now it is widely used in medium and low grade car model.

3. Ic regulator (Integrated circuit regulator)

In addition to the advantages of the transistor regulator, the integrated circuit regulator has an ultra-small size and is installed inside the generator (also known as a built-in regulator), which reduces the external wiring and improves the cooling effect. It is now widely used in Santana, Audi and other car models.

4. Computer controlled regulator

After the total load of the system is measured by the electric load detector, a signal is sent to the generator computer, and then the generator voltage regulator is controlled by the engine computer, and the magnetic field circuit is turned on and off in a timely manner, thereby reliably ensuring the normal operation of the electrical system, the battery is fully charged,  and can reduce engine load and improve fuel economy. Such regulators are used on car generators such as Shanghai Buick and Guangzhou Honda.


Operation and maintenance

The regulator is generally not allowed to remove the cover during the operation. Normally, a comprehensive inspection and maintenance is performed every 200 hours of operation. The contents are as follows:

1) Remove the cover and check the contact surface for dirt and burning loss. If there is dirt, wipe the contact surface with a clean paper. If the contact is ablative or the surface is not flat and the contact is poor, generally use "00" sandpaper or sand strip to grind it, and then clean it with clean paper.

2) Check the fastness of each connector and measure the resistance and resistance value of each coil. If there is any damage, repair or replace new ones in time.

3) Check  the closing voltage and reverse current of the current interrupter, the limiting voltage and the limiting current of the throttle, and the gap and air gap of various contacts. If it does not meet the requirements, it should be adjusted.

4) Check the adjusted regulator and pay attention to the indication of the charging ammeter pointer when starting the diesel engine. If the pointer of the ammeter is still pointing to the "-" side when the diesel engine operates at a moderate speed, it indicates that the contact of the current breaker is not disconnected, the earthing switch should be quickly disconnected; otherwise, the battery, regulator and charging generator will be damaged. If the pointer of the ammeter still points to "0" after the diesel engine starts to the rated speed, it shows that the adjustment is not adjusted according to the technical requirements, should be checked and adjusted again.

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